1. Technical Field
The present invention relates to a radio communication device and, more particularly, to a radio communication device capable of transmitting an optimum radio output in accordance with a usage mode.
2. Background Art
Conventionally, a booster (radio output amplifier) is generally connected to a portable telephone to enhance a radio output.
For example, referring to FIG. 1, a radio communication device disclosed in Japanese Patent Laying-Open No. 8-65365 includes a portable telephone 116 and a booster 117 connected to each other via an RF (Radio Frequency) signal line 118 and a control signal line 119.
Portable telephone 116 includes an antenna 5, a transmission circuit 2 for transmitting an output signal, an output control circuit 4 for controlling an output of transmission circuit 2, a switch 120 connected to transmission circuit 2, for receiving the output signal of the transmission circuit 2 as an input and leading the output signal to booster 117 via RF signal line 118 or to antenna 5 on the basis of a selection signal from a control circuit to be described hereinafter, and a control circuit 103 connected to output control circuit 4 and the switch 120, for controlling output control circuit 4 and supplying the selection signal to switch 120.
Control circuit 103 includes an amplification level storing device 121, a maximum transmission output storing device 122, a connection detecting circuit 123, and a CPU (Central Processing Unit) 107.
Booster 117 includes an output amplifying circuit 124 for amplifying an output signal received from portable telephone 116 via RF signal line 118, an output control circuit 125 connected to output amplifying circuit 124, for controlling an output from the output amplifying circuit, an antenna 127 connected to output amplifying circuit 124, and a control circuit 126 connected to control signal line 119 and output control circuit 125, for controlling output control circuit 125.
Control circuit 126 includes an amplification level storing device 128 and a CPU 129 connected to amplification level storing device 128.
When booster 117 is connected to portable telephone 116, the connection of booster 117 is detected by connection detecting circuit 123 in portable telephone 116. In CPU 107 in portable telephone 116, information indicating whether portable telephone 116 is in a call mode or a standby mode is stored. According to the information, CPU 107 determines whether portable telephone 116 is in the call mode or standby mode at the time when booster 117 is connected to portable telephone 116.
When it is determined that booster 117 is connected during a call, on portable telephone 116 side, by an instruction of CPU 107, information indicating that portable telephone 116 and booster 117 are connected is transmitted from control circuit 103 to booster 117 via control signal line 119. CPU 107 transmits information of a necessary amplification level on booster 117 side, which is stored in amplification level storing device 121 to booster 117 via control signal line 119. Further, CPU 107 calculates a transmission output value obtained by subtracting an output level stored in amplification level storing device 121 from an output level stored in maximum transmission output storing device 122 set at the start of a call. On the basis of the transmission output value, control circuit 103 transmits a control signal to output control circuit 4. Output control circuit 4 controls transmission circuit 2 so as to set the transmission output to a desired level.
As a result, the output whose level has been changed is output from transmission circuit 2. Simultaneously, control circuit 103 controls switch 120 to switch the direction of the radio signal from antenna 5 of the portable telephone to RF signal line 118. The radio signal is supplied to output amplifying circuit 124 in booster via RF signal line 118.
When control circuit 126 in booster 117 receives information that portable telephone 116 and booster 117 are connected to each other during a call from portable telephone 116 via control signal line 119, control circuit 126 notifies CPU 129 of the information. Further, when control circuit 126 receives the amplification level information from portable telephone 116, control circuit 126 stores the information into amplification level storing device 128. On the basis of the amplification level information stored in amplification level storing device 128, CPU 129 controls output amplifying circuit 124 via output control circuit 125. Output amplifying circuit 124 transmits the amplified output signal from antenna 127.
In such a manner, a radio output control for controlling an output so as to not exceed a maximum transmission output which is set at the time of start of a call even when portable telephone 116 is connected to booster 117 during a call can be realized. That is, in the radio communication device, according to a mechanical difference whether antenna 5 of portable telephone 116 is used or antenna 127 of booster 117 is used, the maximum transmission output value of an output signal is adjusted.
In the device, however, when an output signal is desired to be changed to an optimum transmission output value according to a usage mode such as a mode of using the device on a desk or a mode of using the device by applying the portable telephone to an ear of the user, there is a problem that such a control cannot be performed.